This invention relates to a refrigeration system for effecting cooling by evaporation of water or heating by condensation of water vapor.
A heat pump is conventionally known which effects cooling and heating with the use of evaporation and condensation of water, as disclosed in Japanese Unexamined Patent Publication 6-257890.
In its cooling operation, the heat pump supplies a water to a vacuum container held in a reduced-pressure condition (for example, at about 4 to 5 mmHg), and generates a cold water by allowing the water stored in the vacuum container to voluntarily evaporate. The generated cold water is raised in pressure to the atmospheric pressure by a pump, taken out of the vacuum container and used for cooling.
In its heating operation, the heat pump supplies a water heat-exchanged with a water of heat source to the vacuum container and evaporates it therein. The water vapor in the vacuum container is compressed by a compressor, and pumped to a condenser. The water vapor has a lower pressure than the atmospheric pressure even after compressed. Water circulates through a flow passage of the condenser. The water inside of the flow passage is heat-exchanged with the water vapor outside of the flow passage, and thereby heated with heat of condensation of the water vapor. The generated hot water is used for heating.
Problems to be Solved
In this case, if the water stored in the vacuum container is merely evaporated, evaporation of water occurs only in the water surface area in the vacuum container. Therefore, in order to enhance evaporation in the vacuum container, it is necessary to upsize the vacuum container to extend the water surface area. Since the vacuum container requires high pressure resistance, however, it is extremely disadvantageous in terms of fabrication cost to upsize the vacuum container. To cope with this problem, in the heat pump as described above, attempt is made to enhance evaporation by spreading water inside of the vacuum container. In this manner, however, the water surface area is slightly extended by disturbance, which is not sufficient to enhance evaporation.
Also, in the above heat pump, a cold water in the vacuum container is extracted by raising the pressure thereof with a pump for the purpose of application of the generated cold heat. Pumping up the cold water from the vacuum container in reduced-pressure condition, however, is likely to cause cavitation inside of the pump, because the inside of the vacuum container is under extremely low pressure as described above. Therefore, the above heat pump has a problem in that the pump is damaged due to cavitation thereby providing deteriorated reliability.
As an approach to the above problem, it can be contemplated to provide a heat transfer pipe inside of the vacuum container, channel a water through the heat transfer pipe, cool the water inside of the pipe with a cold water outside of the pipe, and thereby extract cold heat. In fact, however, it is difficult to cool the water inside of the pipe down to the same temperature as that of the cold water outside of the pipe. This presents another problem that cold heat cannot sufficiently be extracted from the water inside of the pipe.
Further, the above problem is also created when hot heat is extracted in the condenser. Specifically, even when the condenser is provided with a flow passage and a water inside of the flow passage is heated up with water vapor outside thereof, as is the case with the above heat pump, there is a problem that hot heat cannot sufficiently be extracted due to heat loss during heat exchange.
There is conventionally known a moisture permeable membrane which does not permeate water as a liquid but can permeate water vapor as a gas. No application of a moisture permeable membrane of such kind for the condenser has been found. Accordingly, the appearance of a novel system using such a moisture permeable membrane would be desirable.
The present invention has been made in view of the foregoing points, and an object thereof is, in a refrigeration system using phase changes of water, to provide a downsized evaporator for evaporating water under reduced pressure, enhance reliability by facilitating the extraction of cold heat from the evaporator, and apply a moisture permeable membrane for a condenser.
A first solution taken in the invention is directed to a refrigeration system for cooling a heat transfer medium by evaporating water of the heat transfer medium in an evaporator (11). Further, the system is provided with: the evaporator (11) which is formed of a container-like member (55) having an inner space divided into a liquid side space (12) and a gas side space (13) by a moisture permeable membrane (14) capable of permeating water vapor, the liquid side space (12) being filled with the heat transfer medium which is water or water solution; and evacuating means (20) for evacuating from the gas side space (13) water vapor which has been provided by evaporation of water from the heat transfer medium in the liquid side space (12) of the evaporator (11) and has moved to the gas side space (13), and for holding the gas side space (13) into a predetermined reduced-pressure condition.
In a second solution taken in the invention, the refrigeration system in the first solution further includes a condenser (15) which is formed of a container-like member (55) and arranged to allow the water vapor evacuated from the evaporator (11) by the evacuating means (20) to flow into a gas side space (17) thereof and then move from the gas side space (17) to a heat transfer medium with which a liquid side space (16) thereof is filled.
A third solution take in the invention is directed to a refrigeration system which is provided with: an evaporator (11) in which a heat transfer medium of water or water solution is stored; evacuating means (20) for evacuating water vapor provided by evaporation of water from the heat transfer medium inside of the evaporator (11) and for holding the evaporator (11) in a predetermined reduced-pressure condition; and a condenser (15) formed of a container-like member (55) an inner space of which is divided into a liquid side space (12) and a gas side space (13) by a moisture permeable membrane (14) capable of permeating water vapor, the condenser (15) being arranged to move the water vapor admitted into a gas side space (17) thereof by the evacuating means (20) to a heat transfer medium with which a liquid side space (16) thereof is filled.
In a fourth solution taken in the invention, the refrigeration system in the second or third solution is arranged to effect a heat pumping operation of using heat released from the water vapor in the condenser (15) to heat the heat transfer medium.
In a fifth solution taken in the invention, the refrigeration system in any one of the first to fourth solutions is arranged so that the evacuating means (20) comprises a compressor (21) for compressing the water vapor sucked from the evaporator (11) and pumping the water vapor into the condenser (15).
In a sixth solution taken in the invention, the refrigeration system in any one of the first to fourth solutions is arranged so that the evacuating means (20) comprises an absorbing medium for absorbing and releasing moisture, allows the absorbing medium to absorb the water vapor from the evaporator (11) and sends into the condenser (15) the water vapor released from the absorbing medium.
In a seventh solution taken in the invention, the refrigeration system in any one of the first to fourth solutions is arranged so that the evacuating means (20) includes water vapor generating means (115) for generating water vapor through the application of heat and an ejector (110) for ejecting water vapor from the evaporator (11) under the action of a jet of the water vapor generated by the water vapor generating means (115).
In an eighth solution taken in the invention, the refrigeration system in any one of the first to seventh solutions is arranged so that the container-like member (55) contains a multiplicity of moisture permeable tubes (60) each formed of a moisture permeable membrane (14, 18), the inside of the moisture permeable tube (60) is formed into a liquid side space (12, 16) and the outside of the moisture permeable tube (60) is formed into a gas side space (13, 17).
In a ninth solution taken in the invention, the refrigeration system in any one of the first to eighth solutions is arranged so that the moisture permeable membrane (14, 18) in the container-like member (55) has a surface which is presented to the gas side space (13, 17) and covered with a porous film (61).
In a tenth solution taken in the invention, the refrigeration system in any one of the first to ninth solutions is arranged so that the moisture permeable membrane (14, 18) in the container-like member (55) has water repellency.
In an eleventh solution taken in the invention, the refrigeration system in any one of the first to tenth solutions is arranged so that the evaporator (11) cools the heat transfer medium to generate a frozen product slurry.
In a twelfth solution taken in the invention, the refrigeration system in the eleventh solution is arranged to include a heat storage tank (67) and effect a heat storage operation of storing in the heat storage tank (67) the frozen product generated by the evaporator (11).
In a thirteenth solution taken in the invention, the refrigeration system in any one of the two to tenth solutions is arranged to include a heat storage tank (67) and effect a heat storage operation of storing in the heat storage tank (67) the heat transfer medium cooled by the evaporator (11) and a heat utilization operation of cooling the heat transfer medium in the evaporator (11) and supplying to the condenser (15) the heat transfer medium stored in the heat storage tank (67) through the heat storage operation to condense water vapor.
In a fourteenth solution taken in the invention, the refrigeration system in any one of the first to tenth solutions further includes: a heat storage tank (67) connected to the evaporator (11) to allow the heat transfer medium to circulate between the evaporator (11) and the heat storage tank (67); and heat utilization means (32) to which the heat transfer medium is supplied from the evaporator (11), and the system is arranged to effect a heat storage operation of storing in the heat storage tank (67) the heat transfer medium cooled by the evaporator (11) and a heat utilization operation of supplying to the evaporator (11) the heat transfer medium stored in the heat storage tank (67) through the heat storage operation and supplying to the heat utilization means (32) a frozen product slurry produced by cooling the heat transfer medium.
In a fifteenth solution taken in the invention, the refrigeration system in any one of the two to tenth solutions further includes: a heat utilization side heat exchanger (32) for heat exchanging the heat transfer medium with an object to be cooled; and a cooling tower (90) for cooling the heat transfer medium, and the system is arranged to effect a first cooling operation of circulating the heat transfer medium between the cooling tower (90) and the condenser (15), circulating the heat transfer medium between the heat utilization side heat exchanger (32) and the evaporator (11) and operating the evacuating means (20) and effect a second cooling operation of circulating heat transfer medium between the cooling tower (90) and the heat utilization side heat exchanger (32) and stopping the evacuating means (20).
Operations
In the first solution, the evaporator is formed of a container-like member (55). The liquid side space (12) of the container-like member (55) as the evaporator (11) is filled with a heat transfer medium. The gas side space (13) is held at a predetermined pressure lower than the atmospheric pressure by the evacuating means (20). Namely, in the evaporator (11), only the gas side space (13) is reduced in pressure, while the liquid side space (12) is at atmospheric pressure. Water is evaporated from the heat transfer medium in the liquid side space (12), and the water vapor passes through the moisture permeable membrane (14) and moves to the gas side space (13). The water vapor in the gas side space (13) is evacuated by the evacuating means (20) so that the pressure of the gas side space (13) is held. On the other hand, the heat transfer medium in the liquid side space (12) is cooled by loosing latent heat of evaporation. Then, cold heat is extracted by taking out the cooled heat transfer medium from the liquid side space (12).
In the second solution, the condenser (15) is provided. This condenser (15) condenses water vapor evacuated from the evaporator (11) by the evacuating means. The condenser (15) is formed of a container-like member (55). The water vapor is supplied from the evacuating means to the gas side space (17) of the container-like member (55) as the condenser (15). The water vapor moves to the liquid side space (16) through the moisture permeable membrane (18) and condenses through the contact with the heat transfer medium with which is filled the liquid side space (16).
In the third solution, the inside of the evaporator (11) is held in a reduced-pressure condition, and water evaporates from the heat transfer medium stored in the evaporator (11). The condenser (15) is formed of a container-like member (55). The water vapor in the evaporator (11) is sent into the gas side space (17) of the container-like member (55) as the condenser (15) by the evacuating means (20). The water vapor in the gas side space (17) moves to the liquid side space (16) through the moisture permeable membrane (18) and condenses through the contact with the heat transfer medium with which is filled the liquid side space (16).
In the fourth solution, a heat pumping operation is performed. Specifically, when water vapor condenses in the condenser (15), water vapor releases heat of condensation. The heat of condensation released from the water vapor is used to heat the heat transfer medium.
In the fifth solution, the evacuating means (20) is composed of a compressor (21). Water vapor in the evaporator (11) is sucked into the compressor (21) so that the inside of the evaporator (11) is held at a predetermined pressure. The compressor (21) compresses the water vapor sucked by itself and then pumps it into the condenser (15).
In the sixth solution, the evacuating means (20) is provided with an absorbing medium. The evacuating means (20) sucks water vapor from the evaporator (11) by causing the absorbing medium to absorb the water vapor. Thus, the inside of the evaporator (11) is held at a predetermined pressure. Further, the evacuating means sends into the condenser (15) the water vapor released from the absorbing medium. In other words, the water vapor evacuated from the evaporator (11) is sent into the condenser (15) via the absorbing medium.
In the seventh solution, the evacuating means (20) is composed of water vapor generating means (115) and an ejector (110). Relatively high-pressure water vapor, which has been generated by the water vapor generating means (115), is sent into the ejector (110) and ejected therefrom at a high speed. Then, a high-speed water vapor jet produced by the ejector (110) causes the water vapor in the evaporator (11) to be sucked into the ejector (110) and evacuated therefrom.
In the eighth solution, the inner space of the container-like member (55) is divided into liquid side spaces (12, 16) and gas side spaces (13, 17) by the multiplicity of moisture permeable tubes (60). The inside of each moisture permeable tube (60) is formed into the liquid side space (12, 16), while the outside thereof is formed into the gas side space (13, 17). Therefore, the surfaces of all of the multiplicity of moisture permeable tubes (60) form gas-liquid interfaces from which water of the heat transfer medium is evaporated.
In the ninth solution, one surface of the moisture permeable membrane (14, 18) is covered with a porous film (61). For example, if the container-like member (55) is used as the evaporator (11), water vapor provided by evaporation of the heat transfer medium in the liquid side space (12) passes through the moisture permeable membrane (14) and further pores of the porous film (61), and then moves to the gas side space (13).
In this respect, a pressure difference exists between the liquid side space (12, 16) and the gas side space (13, 17) in the container-like member (55). Therefore, the moisture permeable membrane (14, 18) is desired to have a sufficient strength to accommodate the pressure difference. In this solution, however, a two-layer structure is constituted by the moisture permeable membrane (14, 18) and the porous film (61). Therefore, the structure ensures a sufficient strength to accommodate the pressure difference between the liquid side space (12, 16) and the gas side space (13, 17) while permeating water vapor well.
In the tenth solution, the moisture permeable membrane (14, 18) is formed to have water repellency. In other words, water is repelled on the surface of the moisture permeable membrane (14, 18). Accordingly, even when the heat transfer medium is cooled by evaporation to generate a frozen product, such a frozen product never sticks to the surface of the moisture permeable membrane (14).
In the eleventh solution, evaporation of water in the evaporator (11) cools the heat transfer medium to produce a frozen product.
In the twelfth solution, cold heat is accumulated by storing in the heat storage tank (67) the frozen product produced by the evaporator (11).
In the thirteenth solution, cold heat is accumulated by storing in the heat storage tank (67) the heat transfer medium cooled by the evaporator (11). During the heat utilization operation, the system generates cold heat by evaporating water in the evaporator (11) and concurrently supplies to the condenser (15) the heat transfer medium stored in the heat storage tank (67) through the heat storage operation. In other words, cold heat stored in the heat storage tank (67) is used to condense water vapor in the condenser (15).
In the fourteenth solution, cold heat is accumulated by storing in the heat storage tank (67) the heat transfer medium cooled by the evaporator (11). During the heat utilization operation, the system supplies to the evaporator (11) the heat transfer medium stored in the heat storage tank (67) through the heat storage operation, and further cools it to produce a frozen product slurry. The produced frozen product slurry is supplied to the heat utilization means (32) so as to be used for the purpose of cooling an object to be cooled or other purposes. Specifically, if the frozen product slurry is allowed to stand stored in the heat storage tank (67), it will not in due course be circulated in the form of a slurry due to cohesion of its particles. In this solution, however, the frozen product is produced during the heat utilization operation and can be therefore utilized in the form of a slurry capable of circulation.
In the fifteenth solution, the first and second cooling operations are made. The first cooling operation is performed at large cooling loads and is that of supplying to the heat utilization side heat exchanger (32) a relatively low-temperature heat transfer medium cooled by the evaporator (11) and thereby cooling an object to be cooled. On the other hand, the second cooling operation is performed at small cooling loads and is that of supplying to the heat utilization side heat exchanger (32) a heat transfer medium cooled by only the cooling tower (90) and thereby cooling an object to be cooled.
Effects
In the first solution, the evaporator is formed of a container-like member (55). Accordingly, in the evaporator (11), only the gas side space (13) is reduced in pressure while the liquid side space (12) is at atmospheric pressure. Therefore, a cooled heat transfer medium can easily be extracted from the liquid side space (12). Specifically, it is necessary for the prior art to raise the pressure of the heat transfer medium in reduced-pressure condition and then extract it, whereas it is necessary for this solution only to extract the heat transfer medium in atmospheric pressure condition from the evaporator (11). Therefore, there is no need for the mechanism that raises the pressure of the heat transfer medium for the purpose of extracting cold heat, which simplifies the system. Further, even when a pump or the like is used to give the heat transfer medium a conveying force, no special consideration is needed of cavitation, unlike the prior art.
Further, the evaporator (11) is formed of a container-like member (55) and the moisture permeable membrane (14) forms a gas-liquid interface in the evaporator (11). Therefore, the form of the gas-liquid interface can be arbitrarily set by changing the shape of the moisture permeable membrane (14). For example, if the moisture permeable membrane (14) is defined in a cornice shape or the like, the area of the gas-liquid interface can be increased. Accordingly, the area of the gas-liquid interface can be increased while the evaporator (11) is kept in a small size. This enhances evaporation of water from the heat transfer medium.
In the second to fourth solutions, the condenser (15) is formed of a container-like member (55). Accordingly, water vapor in the gas side space (17) can move to the liquid side space (16) through the moisture permeable membrane (18), and the water vapor can condense through the contact with the heat transfer medium in the liquid side space (16). Therefore, as compared with the case where heat exchange is made through indirect contact between water and water vapor as in the prior art, heat loss due to heat exchange can be reduced thereby providing enhanced efficiency. Particularly in the fourth solution, a heat pumping operation is provided using heat of condensation.
In the eighth solution, the moisture permeable tubes (60) define liquid side spaces (12, 16) and gas side spaces (13, 17). Therefore, if the container-like member (55) is used as the evaporator (11), the area of the gas-liquid interface in the evaporator (11) can largely be increased without upsizing the evaporator (11). As a result, evaporation of water from the heat transfer medium can be well enhanced, and a sufficient cooling capacity can be attained while the evaporator (11) is kept in a small size. Further, also when the container-like member (55) is used as the condenser (15), condensation can be enhanced thereby providing a downsized condenser (15).
According to the ninth solution, the two-layer structure made up of the moisture permeable membrane (14, 18) and the porous film (61) ensures strength. Therefore, any trouble from breakage of the moisture permeable membrane (14, 18) can be obviated, which enhances reliability.
According to the tenth solution, a container-like member (55) well adapted especially for an evaporator (11) for producing a frozen product can be formed by using a repellent moisture permeable membrane (14, 18). Specifically, if a frozen product sticks to the moisture permeable membrane (14), this blocks permeation of water vapor. In this solution, however, sticking of the frozen product to the moisture permeable membrane (14) can be prevented, which provides sufficiently ensured evaporation of water from the heat transfer medium.
According to the eleventh to fifteenth solutions, various operations such as production of a frozen product and heat storage can be effected. Particularly in the fifteenth solution, even if the cooling load varies, an optimal operation according to the cooling load can be performed by separately using the cooling operation via the evaporator (11) and the cooling operation via the cooling tower (90).